Non-flammable Quasi-Solid Electrolyte and Lithium Secondary Batteries Containing Same

Abstract

A rechargeable lithium cell comprising a cathode, an anode, a non-flammable quasi-solid electrolyte containing a lithium salt dissolved in a mixture of a liquid solvent and a liquid additive having a salt concentration from 1.5 M to 5.0 M so that said electrolyte exhibits a vapor pressure less than 0.01 kPa, a vapor pressure less than 60% of the vapor pressure of the liquid solvent alone, a flash point at least 20 degrees Celsius higher than the flash point of the liquid solvent alone, a flash point higher than 150° C., or no flash point, wherein the liquid additive is selected from Hydrofluoro ether (HFE), Trifluoro propylene carbonate (FPC), Methyl nonafluorobutyl ether (MFE), Fluoroethylene carbonate (FEC), Tris(trimethylsilyl)phosphite (TTSPi), Triallyl phosphate (TAP), Ethylene sulfate (DTD), 1,3-propane sultone (PS), Propene sultone (PES), Diethyl carbonate (DEC), Alkylsiloxane (Si—O), Alkylsilane (Si—C), liquid oligomeric silaxane (—Si—O—Si—), Tetraethylene glycol dimethylether (TEGDME), or a combination thereof.

Description

FIELD OF THE INVENTION[0001]The present invention provides a non-flammable electrolyte composition and a secondary or rechargeable lithium battery containing such an electrolyte composition.BACKGROUND[0002]Rechargeable lithium-ion (Li-ion), lithium metal, lithium-sulfur, and Li metal-air batteries are considered promising power sources for electric vehicle (EV), hybrid electric vehicle (HEV), and portable electronic devices, such as lap-top computers and mobile phones. Lithium as a metal element has the highest lithium storage capacity (3,861 mAh / g) compared to any other metal or metal-intercalated compound as an anode active material (except Li4.4Si, which has a specific capacity of 4,200 mAh / g). Hence, in general, Li metal batteries (having a lithium metal anode) have a significantly higher energy density than lithium-ion batteries (having a graphite anode).[0003]Historically, rechargeable lithium metal batteries were produced using non-lithiated compounds having relatively high s...

AI Technical Summary

Benefits of technology

[0024]A specific object of the present invention is to provide a rechargeable lithium-sulfur cell based on rational materials and battery designs that overcome or significantly reduce the following issues commonly associated with conventional Li—S cells: (a) dendrite formation (internal shorting); (b) extremely low electric and ionic conductivities of sulfur, requiring large proportion (typically 30-55%) of non-active conductive fillers and having significant proportion of non-accessible or non-reachable sulfur or lithium polysulfides); (

Problems solved by technology

Unfortunately, upon repeated charges and discharges, the lithium metal resulted in the formation of dendrites at the anode that ultimately caused internal shorting, thermal runaway, and explosion.

As a result of a series of accidents associated with this problem, the production of these types of secondary batteries was stopped in the early 1990's giving ways to lithium-ion batteries.

Even now, cycling stability and safety concerns remain the primary factors preventing the further commercialization of Li metal batteries (e.g. Lithium-sulfur and Lithium-transition metal oxide cells) for EV, HEV, and microelectronic device applications.

Again, cycling stability and safety issues of lithium metal rechargeable batteries are primarily related to the high tendency for Li metal to form dendrite structures during repeated charge-discharge cycles or overcharges, leading to internal electrical shorting and thermal runaway.

This thermal runaway or even explosion is caused by the organic liquid solvents used in the electrolyte (e.g. carbonate and ether families of solvents), which are unfortunately highly volatile and flammable.

However, despite these earlier efforts, no rechargeable Li metal batteries have succeeded in the market place.

This is likely due to the notion that these prior art approaches still have major deficiencies.

For instance, in several cases, the anode or electrolyte structures designed for prevention of dendrites are too complex.

In others, the materials are too costly or the processes for making these materials are too laborious or difficult.

Although lithium-ion (Li-ion) batteries are promising energy storage devices for electric drive vehicles, state-of-the-art Li-ion batteries have yet to meet the cost, safety, and performance targets.

Despite the notion that there is significantly reduced propensity of forming dendrites in a lithium-ion cell (relative to a lithium metal cell), the lithium-ion cell has its own intrinsic safety issue.

Although ILs were suggested as a potential electrolyte for rechargeable lithium batteries due to their non-flammability, conventional ionic liquid compositions have not exhibited satisfactory performance when used as an electrolyte likely due to several inherent drawbacks: (a) ILs have relatively high viscosity at room or lower temperatures; thus being considered as not amenable to lithium ion transport; (b) For Li—S cell uses, ILs are capable of dissolving lithium polysulfides at the cathode and allowing the dissolved species to migrate to the anode (i.e., the shuttle effect remains severe); and (c) For lithium metal secondary cells, most of the ILs strongly react with lithium metal at the anode, continuing to consume Li and deplete the electrolyte itself during repeated charges and discharges.

These factors lead to relatively poor specific capacity (particularly under high current or high charge/discharge rate conditions, hence lower power density), low specific energy density, rapid capacity decay and poor cycle life.

Furthermore, ILs remain extremely expensive.

Consequently, as of today, no commercially available lithium battery makes use of an ionic liquid as the primary electrolyte component.

However, the current Li-sulfur products of industry leaders in sulfur cathode technology have a maximum cell specific energy of 400 Wh/kg (based on the total cell weight), far less than what could be obtained in real practice.

In summary, despite its considerable advantages, the rec

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